Experimental study on a pressure-coring technology based on a freeze-core valve for marine hydrate-bearing sediment sampling

Abstract

Recovery of hydrate-bearing sediments under near in situ conditions remains a topic worthy of investigation. To avoid the frequent sealing failures of mechanical valve-based samplers, a freeze-core-valve-based sampler is proposed for pressure-coring sampling in submarine sediment. A series of preliminary experiments were conducted to characterize the freeze-core valve, including the performance of retaining pressure and adaptation to different sediments. The results show that the freeze-core valve exhibited a strong performance in retaining pressure and can be to various sediments without limitations due to sediment conditions, including pore water salinity, clay mineral content, particle size and grain grading. The retained pressure for a 58-mm nominal diameter and 80-mm-long freeze-core valve formed at −40 °C can reach 43 MPa without leakage, which can meet the requirement of the pressure-coring sampling. The pressure retaining performance can be further improved by lowering the freezing temperature or increasing the length of the freezing-core valve. According to the preliminary tests, the sampling technique based on the freeze-core-valve has the potential to solve the problem of the low recovery success rate of gas hydrate sediment cores in the future.